Unit 3 Review

Population

the entire group of individuals we want information about

Census

collects data from every individual in the population

Sample

a subset of individuals in the population from which we actually collect data

Bias

if the value you want to know gets underestimated or overestimated

Convenience sample

chooses the individuals easiest to reach; results in bias

Voluntary response

sample consists of people who choose themselves by responding to a general invitation

Simple random sample (SRS)

consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

Table of random digits

where each entry is equally likely to be any of the 10 digits 0 through 9 and the entries of independent of each other

Choosing and SRS

Label each individual in the population numerically and use the Table to select labels at random

Stratified random sample

classify the population into groups of similar individuals called strata, then choose a separate SRS in each stratum and combine to form the sample

Cluster sample

classify the population of groups of individual located near each other, then choose and SRS of the clusters, and all the individuals in the chosen clusters are included in the sample

Under coverage

occurs when some members of the population cannot be chosen in a sample

Nonresponse

occurs when an individual chosen for the sample can’t be contacted or refuses to participate

Response bias

a systematic pattern of incorrect responses in a sample survey

Wording of questions

the most important influence on the answers given to s

Observational study

observes individuals and measures variables of interest but does not attempt to influence the responses

Experiment

imposes some treatment on individuals to measure their responses; cause and effect

Confounding

occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other

Treatment

a specific condition applied to the individual in an experiment

Experimental units

the smallest collection of individual to which treatments are applied

Subjects

when the units are human beings

Principles of Experimental Design

1. Comparison - design compares 2 or more treatments

2. Random assignment - assign experimental units to treatment to balance the effects of confounding variables

3. Control - keep other variables the same for all groups

4. Replication - use enough units that differences in the effects of the treatments can be distinguished from ones between the groups

Statistically significant

an observed effect so large it would rarely occur by chance

Completely randomized design

treatments are assigned to all experimental units by chance

Control group

receives an inactive treatment or existing baseline treatment

Placebo effect

response to dummy treatment

Double-blind experiment

neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received

Block

a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to treatments

Randomized block design

the random assignment of experimental units to treatments is carried out separately within each block

Matched pairs design

each block consists of a matching pair of similar experimental units